1. Field of the Invention
This invention relates to sanitary rubber compositions or articles having excellent chemical and physical properties and more particularly, it is concerned with a sanitary rubber composition or article comprising a rubber blended with a finely divided polyethylene powder of a superhigh molecular weight. By the sanitary rubber composition or article, we mean rubber articles in contact with foods, rubber closures or plugs for pharmaceutical vessels, rubber products attached to medical instruments, rubber articles used for human bodies and animals and the like, which have some influences upon human bodies and animals directly or indirectly and which are different from industrial rubber articles, tires and foot wears in chemical and physical properties. That is to say, the sanitary rubber article of the present invention includes rubber articles for foods, drugs, cosmetics, veterinary medicines, feeds and radiation protection, which comes under the administration of the Food and Drug Administration.
2. Description of the Prior Art
For rubber closures for drugs, for example, about 30 examination and test items must be satisfied. These items include provisions for solving problems such as the following: (1) if an additive used as an essential component for a synthetic rubber is released from the surface of a product, it becomes added to a medical fluid as fine particles, (2) when a rubber closure of a vial is pierced by an injection needle, rubber pieces are broken off and added to a medical fluid and (3) if an opening is formed when the injection needle pierces the rubber closure, a medical fluid may issue and spoil clothes. Thus, sanitary rubber articles must be prepared so as to satisfy these newly added requirements.
Up to the present time, it has been proposed to add low molecular weight polyethylene to various rubbers (Japanese Patent Publication No. 5973/1960, Canadian Patent No. 846831/1962) and to produce a rubber plug for an injection fluid by blending a natural rubber or synthetic rubber with a fine powder of polyethylene (Japanese Patent Publication No. 8789/1970). In these techniques, however, a fine powder of polyethylene should be used in a proportion of 1 to 10% by weight with carbon black and lithopone (ZnS+BaSO.sub.4) as a reinforcing agent, since the bridging efficiency is low and the physical properties of a bridged product are inferior.